Inertial navigation systems (INS) generally involve a system accelerometers to maintain and update the current position and orientation of platforms in motion. Bias errors in accelerometers lead to integrated position errors.
Conventionally, utilizing information from an external navigation signal such as a global positioning system (GPS) can improve the position estimates by removing INS bias errors. The particular linkage between an INS and a GPS to obtain improved position and velocity estimates can vary. However, most methods utilize the known properties of the GPS signal, such as its chip rate and coding sequence along with satellite ephemeris data to augment the INS estimates. The dependency on GPS for precision navigation creates a vulnerability in cases of GPS denial (e.g. GPS outage or jamming).
A similar concept of using a “helper” signal is present in some differential GPS systems where a “helper station” in a known location makes estimates of the necessary corrections and forwards them to the nearby platform.